Rolling mill for producing steel for tubes and thin strip

ABSTRACT

The invention relates to a rolling mill for producing metal strips, preferably steel for tubes and/or thin strip, in which the temperature control can be influenced between the finish stands Fi and Fi+1 using a rapid heating device (induction heater), characterized in that the distance between the stands Fi and Fi+1, between which a rapid heating device is arranged, is 5 to 25 m, and in addition to an induction heater, a roller flattening unit (for example, roller leveler  14 ), and/or shears  8 , and/or a driving roller pair  12 , and/or a descaling sprayer  15  are arranged as additional units between the two stands. The roll stand Fi and/or regions in front of the roll stand Fi further comprise actuators for influencing the strip warping and/or strip ski-up/-down at the strip head.

The invention relates to a rolling mill, in particular, aCSP-installation for producing strips, in particular, steel for tubesand/or thin strips, including a caster for producing thin slabs and arolling mill for rolling a thin slab to a strip or thin strip.

Production of steel strips or steel plates by hot rolling is adequatelydescribed in the state-of-the art. Corresponding disclosures are found,e.g., in a paper of P. Uranga et al., “Improvement of Micro-structuralHomogeneity in Thermo-mechanically Processed Nb Steel by Thin SlabCasting,” 43^(rd) Mechanical Working and Steel Processing Conference,Charlotte, ISS, Vol. 39, pages 511-529; in a paper of Kinkenberg, etal., “Processing of Niobium Microaloy API Grade Steel on a Thin SlabPlant”, Material Science Forum, Vols. 500-501, 2005, pages 253-260; andin a paper of S. V. Subramanian, et al., “Process modeling ofmicro-alloyed steel for near net shane casting” Proc. Of the Int. Conf.on Thermomechanical Processing;” “Mechanics, Microstructure, ed. by E.J. Palmiere et al., The University of Shefield, Shefield 2003, pages148-156.

CSP) (Compact Strip Production)—installations are casting and rollinginstallations in which two separate working steps for production ofsteel strip are closely connected with each other, namely, the castingof liquid steel in thin slabs in the caster and rolling of thin slabs insteel strip in the rolling installation. With this, usually the rollingof the previously cast strand is carried out directly with use of thecasting heat or by adjusting the desired rolling temperature using acompensation furnace or a heating device between the caster and therolling mill.

Conventional rolling mills of a thick slab installation have at leastone roughing stand or heavy-plate stand and a finishing rolling trainarranged after the roughing stand or heavy-plate stand at a distancetherefrom. While in the roughing stand or heavy-plate stand, the thinslab is rolled, usually in a reversing operation, to an intermediatestrip with a predetermined thickness, the rolling in the finishingrolling train takes place in tandem operation, with the finishingrolling train being formed as a continuous rolling train. While thedistance between separate stands of such finishing train is usuallyconstant and usually amounts to 5.5 m, the distance between the roughingstand or heavy-plate stand and the first stand of the finishing train isusually many times greater in order to insure the reversing operation inthe roughing stand or heavy plate stand. In this connection, thedistance between the roughing stand or heavy-plate stand and thefinishing train of about 50 m or more is no rarity.

Conventional rolling mills have, because of a usually alignmentarrangement of the thick slab—extraction roller table of the slabfurnace, the roughing stand or heavy plate stand, and the finishingtrain, a large length, and require powerful stands, so that investmentcosts are high. Energetically, conventional rolling mills are inferiorin comparison with CSP-installations. In particular, during productionof thin strips, the entry temperature in the finishing train is verylow, which makes rolling of thin strips difficult. Also, the productionof steel for tubes in a conventional hot rolling mill, because of thenecessary temperature control, is very time-consuming and reduces theproduction of a conventional rolling mill.

Accordingly, the object of the invention to provide a rolling mill ofthe type described above in which the above-described drawbacks can atleast be reduced. Within the meaning of the invention, the object of theinvention is achieved with a rolling mill having features of claim 1.Advantageous embodiments of the invention are defined by dependentclaims.

The rolling mill according to the present invention, in particular, of aCSP-installation, advantageously consists of a compact rolling mill forproducing metal strips, especially steel for tubes and/or thin strips,and in which the temperature between two, following one anotherfinishing stands Fi and Fi+1 can be influenced by a rapid heatingdevice, in particular, an induction heating device. In addition to therapid heating device, advantageously a straightening unit, preferably, aroller straightening device, and/or shears, or/and, optionally, adescaling sprayer, or another strip cooling device can be arrangedbetween the stands Fi and Fi+1. All of the devices are so compactlylocated that they fit in the spacing between the stands of 5-25 m.Further, the stand Fi is equipped upstream of the rapid heating devicewith actuators for influencing the strip warping and/or theski-phenomenon on the strip head.

Together with the straightening unit, advantageously, the rollerstraightening device, and/or the shears and above-mentioned actuators, areliable passage in a limited space through the rapid heating device, inparticular, induction heating device, can be insured with a minimalclearance in the thickness direction. Dependent on the process, therapid heating device, the shears, and/or the descaling sprayer is (are)used or are displaced sidewise, dependent on the to-be-rolled product,or there, alternatively, a roller table, with or without heatinsulation, or a table can be arranged. Also for carrying out thin striprolling, shears can be provided between the stands, in order to takecare of as straight as possible heads and ends of the deformed strip.

As a result of additional devices between the stands, the normal spacingbetween the stands, e.g., ≧5.5, is increased. In order to eliminate apossible secondary scale formation, advantageously, a single descalingsprayer is provided, which is formed as a compact device and,advantageously, is arranged before the stand Fi+1 behind the rapidheating device. For rolling of strip, with high requirements to surfacequality (e.g., for rolling of thin strips), the descaling sprayer infront of the stand Fi+1 can be activated. During production of tubes,the descaling sprayer can be optionally deactivated or removed from therolling line.

In order to save space, optionally, a looper can be dispensed with and,instead of it, means for regulating tension, with or without a tensionmeasuring roller, can be provided.

In comparison with conventional rolling mills with induction heatingbetween the roughing and finishing trains, the inventive use of arolling mill, preferably, a rolling mill of a CSP-installation withcorresponding additional units, noticeably reduces the space occupied bythe rolling mill. The use of additional units, which are selectivelyinserted in the finishing rolling mill, advantageously improves therolling process as with regard to carrying out the process so withregard to obtaining of a corresponding structure. The additional unitsrequire, according to the invention, little space and are arrangedbetween two finishing stands, the distance between which amounts to 5-25m. On the other hand, the space requirement between two stands withadditional units is much smaller than the length of the intermediatestrip which is rolled there.

Advantageously, a thin strip, which is cast by a caster ofCSP-installation, has a thickness, equal or less than 120 mm. Thereby,there is provided a CSP-installation that alone, without use of areversing roughing stand, and with the use of a number of finishingstands forming a rolling mill, is in a condition to produce a desiredproduction spectrum from a thick tube strip to a thin strip.

As an example and a preferred embodiment, a method and the production ofa tube strip in a CSP-installation will be described. The TM-method(thermomechanical method) in a CSP-installation consists as a rule of astep of one or more deformations of an austenitic initial structure inrecrystallization temperature range for producing a uniform, fine,recrystallized austenite structure, and a following step of one orseveral deformations of the recrystallized, austenitic structure forproducing a high-dislocation, extended in an area as much as possible,non-recrystallized austenite structure (so-called pancake structure).Thus, these steps can be called conditioning of the austenite.

Finally, in a further step, cooling of austenitic structure which hasbeen produced in the first step, is carried out for producing afine-grain structure in the finished hot rolled strip or hot rolledsheet with a phase conversion. The structure of the finished hot rolledstrip or hot rolled sheet consists of a combination of ferrite, perlite,bainite, and martensite, wherein the content of these four structurecomponents can, respectively, amounts to between 0% and 100%.

As a result of the above-described TM-method, it is also possible todispense with the above-mentioned step of deformation in thenon-recrystallized temperature range of the austenite. In this case, theconditioning of the austenite takes place entirely in therecrystallization temperature region of the austenite.

The difficulty with the mechanical hot rolling consists, however, inthat for producing the uniform, fine recrystallized austenite grain inthe recrystallization range, as large as possible deformation should beundertaken. A fine recrystallised structure is distinguished by the factthat not only the former, non-uniform cast structure, but alsoindividual coarse grains or structure regions have to be completelytransformed into a uniform, fine recrystallised structure with smallscatter around the mean grain size. This condition frequently is notfulfilled or is fulfilled incompletely and leads to an inadequatelyconditioned austenite structure.

If a step of hot rolling in the non-crystallization temperature range ofthe austenite follows the step of hot rolling in the recrystallisationtemperature range of the austenite, often only little residualdeformation for the succeeding actions in the thermomechanical treatmentremains when there is a large ratio of the thickness of the finished hotstrip or hot sheet and the thickness of the slab or the intermediatestrip. Even when individual stands are taken out, this, on occasion, isnot sufficient to transform possibly still present residues of the caststructure as well as individual coarse grains or structure regions intoa uniform flat pancake structure of non-recrystallised austenite grains.An insufficiently conditioned austenite is also present in this case.

Inadequately conditioned austenite has the disadvantageous consequencein the finished hot strip or hot sheet consisting in the presence ofindividual coarser grains outside the normal distribution about the meangrain size and/or of structure regions having a substructurecharacterized by small-angle grain boundaries. However, structureregions of that kind lead to deterioration in the mechanical propertiesof the strip or sheet, particularly to a reduced toughness.

In correspondence with the description above of TM-method, thedeformation in the recrystallization range of the austenite is ofcritical importance for the characteristics of the finished steel stripor sheet. The degree of the deformation required in first step of thethermomechanical treatment can, in fact, be replaced in part by anelevated entry temperature. However, this possibility is limited by themaximum furnace temperature as well as by the cooling at the time ofcontact with the roll and by thermal radiation between the stands whenseveral stands participate in this step.

Particularly advantageously is a CSP-installation in which a heatingdevice is arranged between two stands Fi and Fi+1 of the rolling mill,in particular between a first stand F1 and the second stand F2. Ifneeded, the heating device can be removed from the rolling mill andagain inserted therein. A particularly advantageous is an inductionheating device, especially one with one-four induction elements.Altogether, with such heating devices, one strives for a construction ascompact as possible with a high power density. The power density lies,advantageously in a range with at least 1500 mw per square meter,preferably, with about 4,000 mw per square meter, when measuring thepower density that has been just applied to the strip or inducedtherein. As an inductor element, such constructional element isdesignated through which power is applied to the strip. One or severalinduction elements can provide induction heating.

At the end of the installation, the rolling mill, preferably acontinuous rolling mill is used within which the above-described, in theexample, deformation steps are used at high temperature and, if needed,with a support of a heating device between the finishing stands and, atan optional cooling of rolls at lower temperatures. Here, no roughingstand or heavy-plate stand, which is conventional for thick slabinstallations, is used.

Advantageously, the deformation steps are joined together, which meansthat all of the involved stands are simultaneously operated inaccordance with entry of thin slabs or intermediate strips. On thisoccasion, the rolling stands operate in tandem, so that operationally,the thin slab or the intermediate strip simultaneously passes throughcommon rolling stands. Separate stands can be displaced and, thus, wouldnot take part in the deformation operation.

In a continuous operation, a method can be used in which the cast strandneed not be cut in slabs, but rather is continuously, preferably,through a tunnel furnace, is fed to a hot rolling mill, is rolled in ahot rolled strip, is separated before a reel, and is wound in a coil.This process prevents accumulation of scrap as no head or foot ends of astrip are produced. In addition, even thinner strips with advantageouslya thickness less than 1 mm can be produced because the danger of a rise(hills) during entry of a thinner strip in the last stand of the hotrolling mill at the start is reduced. During continuous rolling, thefeeding speed of the first active stand is reduced to the casting speedwhich can lead to increased temperature losses before and/or during thehot rolling process. However, for rolling, high rolling temperaturesand, thus, heating of the strip is necessary to avoid rollingtemperatures in the ferrite phase and/or the two-phase area austeniteplus ferrite.

One of such method and appropriate apparatuses permit in principle theproduction of different steels with a reduced austenite phase area,e.g., with silicon content of more than 1%. For this, for rolling,higher rolling temperatures are necessary to reliably avoid rollingtemperatures in the ferrite phase and/or the intermediate phaseaustenite plus ferrite. Such steel goods can be produced, withoutfurther addition, on the inventive CSP-installation.

During the production of strips or thin strips, as discussed above,advantageously an induction heating is provided between the front standsor at least in the region between the front stands. Advantageously, theinduction heating is provided between the first and second or/and thesecond and third stands of the finishing mill.

The induction heating, however, is characterized by a comparativelysmall penetration in the thickness direction and is a sensiblecomponent. During rolling in a finishing mill, in particular in thefirst stand, often, so-called skis, or other such strip cambers, orunflatness are present on the head, which endanger passage of tubestrips or thin strips through the induction heating means or other units(shears, descaling sprayer) between two finishing stands. Besides, theabove-mentioned ski-up or ski-down phenomenon makes the insertion of thepre-rolled intermediate strip in a following stand very difficult. In anunfavorable case, the intermediate strip can damage the units betweenthe two finishing stands.

The reduction or elimination of skis can, e.g., be carried out withhold-down rollers or bending and straightening devices. However, it ismost advantageous when in the inventive installation, the pre-rolledintermediate strip heads are cut off by a suitable cutting device.Optionally, with such a cutting device, both the head and the end of apre-rolled intermediate strip can be cut off when thin finished stripsare produced in a batch operation.

In a further advantageous embodiment of the inventive installation,dependent on the rolled strip material, descaling means can be arrangeddownstream, in the rolling direction, of the heating means for heatingthe intermediate strip, if necessary, after the strip passes through theheating device and the downstream located drive roller pair and beforethe intermediate strip enters in one or several finishing rollingstands. Thereby, it is insured that an almost impurities-free thin stripor a tube strip can be finish-rolled, without the scale damaging thesurface of the strip or thin strip.

In order to insure a reliable passage of the intermediate strip throughthe devices between two finishing stands, there is provided, accordingto the invention, a number of possible control elements which can beused separately or in any arbitrary combination.

The rolling stand itself can have a twin drive and different speedsettings on the upper and lower rolls dependent, e.g., on an entrythickness, thickness reduction, material or the temperature, anddifferent diameters of the upper and lower working rolls.

For influencing the temperature distribution of the rolled product inthickness direction, the adjustment of slab and strip cooling before therolling stand Fi can be carried out so that as symmetrical as possibletemperature profile over the thickness of the rolled stock is provided,or by a well-aimed temperature trimming, the ski-phenomenon isinfluenced. Alternatively, to this end, trimming of the slabtemperatures on upper and lower sides is possible in front of a standwith a heating device.

There is further provided for table height adjustment before thefinishing sand Fi so that a predetermined slab entry position into theroll gap (e.g., the rolling stock middle=rolling gap middle) is reliablyestablished.

The occurrence of a non-linear strip run (ski, amber, curvature) can beparticularly easily prevented by using a straightening unit. This devicefor correction or prevention of skis or strip camber in form of astraightening unit can be, in addition to a roller straighteningmachine, also a hold-down roller, a hold-down plate, a hold-down strut,a bending and straightening machine, a strip head-straightening channel,a strip head pressing device.

As it has already been discussed above, a ski can be cut off the rollingstock with shears.

Finally, occurrence of unevenness in the intermediate strip, inparticular before the entry into the heating device can be detectedadvantageously with suitable surface distance sensors. Suitable sensorssuch as mechanical, optical, or the like are known to one of ordinaryskill in the art. Based on the alarm signal, control means which isconnected with the sensors, can initiate appropriate measures foreliminating or reducing the detected non-linear strip run, or turn theintermediate strip or slab back.

Not only the heating device can protect the above-described devices fromdamage by strip curvatures, but also the damage, in particular producedby induction heating as a result of cooling water remaining on the stripor thin strip, can be minimized by using suitable blowers advantageouslylocated between the rolling stands of the inventive finishing rollingmill or inserted therebetween.

The above-mentioned auxiliary units and measures for ski-elimination canbe used preferably in a CSP-finishing mill for different application.However, they can also be inserted between the finishing stands of aconventional rolling mill.

Induction heating and auxiliary units can be fixedly arranged ordisplaced in and out from the rolling line. As a substitute for themovable units, a heat insulation hood is provided.

The invention will now be explained in detail below with reference tothe drawings which show several embodiments of the inventiveCSP-installation. The drawings show:

FIG. 1 a first embodiment of the invention in which induction heatingmeans and a driving roller pair are arranged between two stands of aschematically shown strip hot rolling mill;

FIG. 2 a second embodiment of the invention with a device forcorrection/prevention of a ski-phenomenon on the intermediate strip headwhich is arranged upstream of the heating device in a strip rollingdirection;

FIG. 3 a third embodiment of the inventive hot rolling mill in which aheating device is arranged between a device for correction/prevention ofa ski-phenomenon on the intermediate strip head and a descaling sprayer,with all three being located between two rolling stands of a hot rollingmill;

FIG. 4 a fourth embodiment of an inventive hot rolling mill witharranged one after another, in the rolling direction shears, rapidheating means, driving rollers, and descaler; and

FIG. 5 a fifth embodiment of an inventive hot rolling mill.

FIG. 1 shows a portion of a hot rolling mill 2 according to the firstembodiment in which a metal strip 1 runs through a first rolling standdesignated as Fi and a second rolling stand designated as Fi+1. Thedistance between the stands Fi and Fi+1 amounts to from 5 m to 25 m.After exiting the finishing stand Fi, the strip 1 runs directly ininduction heating means 8 and, finally, into the driving roller pair 12.This driving roller pair 12 can provide a strip tension (even before thestrip head reaches the following stand) of the strip 1 and, the waterwhich remains on the strip 1, can be easily squeezed. A minimal tensioncontrol can be carried out between the stands Fi and Fi+1. The drivingroller pair 12 helps to precisely adjust the set speed in the standFi+1. Alternatively, a tension measuring roller or a looper (not shown)can be arranged between the stands in order to insure the mass flowrate. Finally, downstream of the rolling stand Fi+1 in the rollingdirection, there is provided a cooling section 11 for cooling the strip1, which was heated in the heating device 8 to a temperature above therecristallization temperature, to a temperature lying in anon-recristallization region. Both devices 8 and 12 can change theirplaces. Also, arrangement of the driving roller pair 12 before or behindthe heating device 8 can be contemplated.

FIG. 2 shows a further embodiment of the hot rolling mill 2 according tothe invention in which again the finishing stand Fi and the finishingstand Fi+1 are shown. Again, a heating device 8 for a rapid heating ofthe metal strip 1 by induction heating is arranged between the rollingstands Fi and Fi+1.

In the rolling direction W, a device 14 for correction/prevention of aski-phenomenon on the intermediate strip that have left the finishingstand Fi, is arranged between the finishing sand Fi and the heatingdevice 8. Such a device 14 for correction/prevention a ski-up or -downcan, e.g., be formed as a bending and straightening driver or as ahold-down roller. Such device 14 should correct a phenomenon of, e.g.,elevated strip head after exiting a rolling stand (a so-called ski-up),i.e., to eliminate or to reduce it to an acceptable achievable minimum.First of all, this serves to prevent downtime resulting from impreciseor non-entry of the intermediate strip head in a following unit, e.g.,the rapid heating device 8, other units (shears, descaling sprayer/oreach further stand Fi+1). In order to prevent the ski-phenomenon, thehot rolling mill according to the invention has a least one rollingstand, preferably, the first rolling stand Fi, with separated and notconnected with each other drives for the upper working roll Fia and thelower working roll Fib. Thereby, with a suitable control of the drives,the ski-up or also ski-down-phenomenon is reduced to a minimum valuealready during rolling.

FIG. 3 shows a third embodiment of the inventive hot rolling mill 2 inwhich between the first shown rolling stand Fi and the second shownrolling stand Fi+1, a rapid heating device 8 follows the device 14 forcorrection of the ski-phenomenon on the intermediate strip head. Betweenthe rapid heating device 8 and the rolling stand Fi+1, a descalingsprayer 15 is arranged with which the scale that sticks to the surfaceof the strip 1, can again be reliably removed. Optionally, thisembodiment of the invention can have a driving roller pair (not shown)and/or a cooling section (not shown).

FIG. 4 shows a fourth embodiment of the inventive hot rolling mill 2 inwhich between the first shown rolling stand Fi and the second shownrolling stand Fi+1, there are arranged, in the rolling direction W ofthe strip 1, shears 13, rapid heating device 8, driving roller pair 12,and descaling sprayer 15. While the rapid heating device 8, the drivingroller pair 12, and the descaling sprayer 15 function in the same way asin the embodiments according to FIGS. 2-4, the shears 13 servesprimarily for cutting off the strip head and, if necessary, the stripend on which rolled tongues or bends (so-called ski) can be formed.Thus, the shears 13 replaces, on one hand, devices shown in previousembodiments (not shown here) for correction/prevention of aski-phenomenon and, in addition, the shears 13 advantageously support afurther rolling process by cutting off the tongues which can adverselyinfluence the running of the strip 1 and the working rolls of thefollowing stands.

In FIG. 5, a fifth embodiment of the inventive hot rolling mill 2 isshown in which there are arranged, in the rolling direction of the strip1, finishing stand Fi, device 14 for correction/prevention of a ski-up,shears 13, and rapid heating device 8. After exiting the rapid heatingdevice 8, the metal strip 1 enters a driving roller pair 12 whichsqueeze the residual water that remained on the metal strip 1. Afterleaving the driving roller pair 12, the metal strip 1 enters thedescaling sprayer 15 in which the residual scale that has formed on thesurface of the strip 1, is reliably removed before entry of the strip 1in the finishing stand Fi+1. Finally, dependent on application, thestrip 1 that have been heated in the rapid heating device 8, can becooled again in the cooling section 11 and be rolled to a finished stripthickness.

The rapid heating device 8 and the shears 13 can be arranged, viewing inthe strip running direction, alternatively or in reverse.

In case the distance between the stands should be further reduced, therapid heating device 8 and the descaling sprayer 15 can be located,viewing in the strip running direction, at the same location and,alternatively, be displaced sidewise in the rolling line so that eitherthe descaling sprayer 15 or the rapid heating device 8 is used.

1. Rolling mill for producing metal strips, preferably steel for tubesand/or thin strip in which a rapid heating device (8) is arrangedbetween two, following one another, finishing stands (Fi, Fi+1),characterized in that distance between the stands (Fi, Fi+1) betweenwhich the rapid heating device (8) is arranged amounts to 5-25 m, andthat in addition to the rapid heating device, at least one furtherauxiliary unit, in particular a straightening unit, preferably a rollerstraightening device (14) (62) is arranged.
 2. Rolling mill according toclaim 1, characterized in that the rolling stand (Fi) which is arrangedbefore the rapid heating device (8), or/and regions before and after therolling stand (1) are equipped with actuators for influencing stripcurvature and/or strip-ski phenomenon on the strip head.
 3. Rolling millaccording to claim 1, characterized in that the rolling stands (Fi,Fi+1) are finishing stands of preferably compact continuous train. 4.Rolling mill according to claim 1, characterized in that itadvantageously forms a rolling mill of CPS-installation for producingthin slabs with a thickness of ≦120 mm.
 5. Rolling mill according toclaim 1, characterized in that the heating device, in particular, aninduction heating device, advantageously, with from 1 to 4 inductionelements, is arranged between the first and second stands (F1, F2)or/and between second and third stands (F2, F3), or is insertabletherebetween.
 6. Rolling mill according to claim 1, characterized inthat at least one driving roller pair is arranged between the stand (Fi)and the following stand (Fi+1) or is insertable therebetween.
 7. Rollingmill according to claim 1, characterized in that a device for correctionor prevention of ski-phenomenon in the intermediate strip is arrangedbetween the stand (Fi) and the following stand (Fi+1), preferably,before the heating device, or is insertable therebetween.
 8. Rollingmill according to claim 7, characterized in that the device forcorrection or prevention of the ski-phenomenon is a hold-down roller, ahold-down plate, a hold-down strut, a bending and straightening machine,a strip held-straightening channel or a strip head-pressing device. 9.Rolling mill according to claim 1, characterized in that at least onerolling stand (Fi) has separate drives for the upper and lower workingrolls (Fia, Fib).
 10. Rolling mill according to claim 1, characterizedin that strip cooling or strip heating means is located before a rollingstand (Fi) with which temperature distribution over the slab or thestrip thickness is adjusted for influencing the ski-phenomenon and stripcurvature.
 11. Rolling mill according to claim 1, characterized in thatthe rolling stand (Fi) has, at a run-in side thereof, tableheight-adjusting means with which the strip running position isadjusted.
 12. Rolling mill according to claim 1, characterized in thatshears are arranged between at least two rolling stands (Fi, Fi+1) orare insertable therebetween.
 13. Rolling mill according to claim 1,characterized in that a descaling sprayer is arranged between at leasttwo rolling stands (Fi Fi+1) or is insertable therebetween.
 14. Rollingmill according to claim 1, characterized in that a distance between two,following one another stands (Fi, Fi+1) is smaller than the intermediatestrip length rolled between the stands.
 15. Rolling mill according toclaim 1, characterized in that a heat insulation hood is arrangedbetween at least two rolling stands (Fi, Fi+1), in particular, as areplacement for previously removed units, or is insertable therebetween.16. Rolling mill according to claim 1, characterized in that the rollingmill is connected with a process model which controls and regulatesdifferent measures and adjustments for influencing the ski-phenomenon.17. Rolling mill according to claim 1, characterized in that the rapidheating device is formed compact and a power density, which is inductedin the strip, amounts to at least 1,500 megawatt per square meter,preferably, to about 4,000 megawatt (+/−18%) per square meter.